Pressure Accumulator, in Particular Pulsation Damper

ABSTRACT

A pressure accumulator, in particular a pulsation damper, having an accumulator homing ( 1 ) which defines a longitudinal axis ( 3 ) and has an inflow opening ( 15 ), and an outflow opening ( 17 ) for a fluid, wherein two working spaces, in particular a gas space ( 23 ) for a working gas and a fluid space ( 33 ), are separated from one another inside the accumulator housing ( 1 ) in a fluid-tight manner, in particular in a gas-tight manner, by a bellows-like separating member ( 21 ), and the separating member ( 21 ) is connected at its one end ( 25 ), to a lid ( 27 ), forming a fixed termination of the gas space ( 23 ) in relation to the housing, and at its other end ( 29 ) to a piston pan ( 31 ) which is axially movable in the accumulator housing ( 1 ) and forms a movable termination of the gas space ( 23 ), such that working movements of the piston part ( 31 ) bring about changes in volume of the working spaces adjoining the separating member ( 21 ), is characterized in that inflow opening ( 15 ) and outflow opening ( 17 ) are respectively provided at the one end and at the other end, opposite one another in the axial direction, of the accumulator housing ( 1 ), such that fluid can flow through the accumulator housing ( 1 ) in its longitudinal direction and in the direction of the working movement of the piston part ( 31 ).

The invention relates to a pressure accumulator, in particular apulsation damper, having an accumulator housing which defines alongitudinal axis and which has an inlet opening and an outlet openingfor a fluid, two working chambers, in particular a gas chamber for theworking gas and a fluid chamber, within the accumulator housing areseparated fluid-tight, in particular gas-tight from one another by abellows-like separating element, and the separating element on its oneend is connected to a cover which forms a housing-mounted termination ofthe gas chamber, and on its other end to a piston part which is axiallymovable in the accumulator housing, and which forms a movabletermination of the gas chamber so that working movements of the pistonpart cause volume changes of the working chambers which border theseparating element.

Pressure accumulators of this type are known, cf. DE 10 2004 004 341 A1.Preferably such pressure accumulators are used to dampen pressurefluctuations in hydraulic systems in order to protect measurement andcontrol means, filters and other components integrated in the systemagainst damaging pulsations.

One preferred area of application is the use as pulsation dampers in theinjection systems of internal combustion engines, especially largediesel engines aboard ships or in block-type thermal power stations. Inthis connection pressure fluctuations occur both in the fuel feed systemand also in the fuel return system, the frequency and intensity of thepulsations being determined by the sequence of injection processes whichcomprise removal of fuel from the system, compression, injection bymeans of high pressure injection pumps and re-opening of the connectionto the system. For an 8-cylinder, four-stroke engine this frequency is,for example, 40 Hz at a speed of 600 rpm, and depending on theproperties of the system, the given fuel delivery pressures and themanner of operation of the high pressure pumps, pressure peaks of morethan 50 bar can occur.

Since these fuel systems of conventional design integrate measurementmeans such as viscosimeters, temperature measuring devices and the likewhich are sensitive to pressure fluctuations, it is important toeliminate or at least reduce the pressure fluctuations.

Accordingly, the object of the invention is to devise a pressureaccumulator which in spite of a compact construction is characterized byespecially good damper action.

According to the invention, this object is achieved by a pressureaccumulator which has the features of claim 1 in its entirety.

According to the characterizing part of claim 1, one essential inventiveparticularity vis-à-vis the prior art consists in that an in-lineconstruction is implemented for which both fluid ports, the inletopening and the outlet opening, lie on one axis. Compared to the knownsolutions, for which on one end of the accumulator housing there is aflow deflection block on which both fluid ports are located and in whichinner deflection surfaces dictate a flow path for the inflowing fluidand outflowing fluid, in the invention the overall length is less andthus the desired construction is compact. The in-line construction alsoenables simpler and more space-saving installation. When the accumulatorhousing, for example, has a cylindrical shape, the pressure accumulatorafter installation looks like an intermediate line piece which differsfrom the base line only in diameter. Since for in-line installation nobending/torsion moments are applied by the pressure accumulator to theline, the number of fasteners may be reduced.

Since there is only one opening on each end of the housing, fluid portsof especially large dimensions are possible, so that much larger flowrates can be implemented than in the prior art. In conjunction with flowthrough the accumulator housing, in its longitudinal direction thisleads to the desired improvement of the damping action.

Preferably the separating element is a metal bellows with a plurality offolds or membrane pairs located over one another; in its interior itborders the gas chamber between the cover and the piston part. Whenusing this metal bellows, almost no gas losses occur. When usingsuitable metals, such as stainless steel, no problems due to corrosivefluids such as diesel oil, heavy oil or biofuels arise. Nor areincreased fuel temperatures a problem, since the corresponding metallicmaterials are resistant to temperatures far exceeding 200° C. Sincethere are weld connections on the metal bellows, the termination isgas-tight without additional seals.

In advantageous embodiments the piston part on its side bordering thefluid chamber has a cavity which enlarges the volume of the fluidchamber. If in this connection the arrangement is such that the pistonpart is made cup-shaped with a circular cylindrical side wall whichextends into the circularly cylindrical interior of the metal bellowsalong the inside of its folds with an immersion depth of variedmagnitude according to the working movements of the piston part, theenlargement of the volume of the fluid chamber at the same timesaccompanies a reduction in the volume of the gas chamber. This yieldsseveral advantages. One the one hand, the choice of the depth of the“cup” enables matching of the ratios of the volumes of the gas chamberto the fluid chamber according to the respective working conditions. Onthe other hand, the special advantage arises that the length of themetal bellows even for a preferable small volume of the gas chamber canbe selected to be relatively long so that it has a plurality of folds.This ensures that the bellows in the execution of alternating movementsis in the region of tolerable material stresses so that it can execute astroke as large as possible with as large a number of repetitions aspossible without compromising operating reliability.

Finally, because the piston part extends in a cup-like manner in theinterior of the metal bellows, the metal bellows is guided and supportedfrom the inside such that the possibilities of angular or lateraldeflection are limited; this protects the metal bellows againstunfavorable operating states and ensures optimum dynamic behavior.

In one especially simple and economical construction, the accumulatorhousing is a circularly cylindrical tubular body in which the metalbellows is concentrically held with the formation of an annulus betweenthe inside wall of the tubular body and the outside of the metal bellowsand the annulus forms part of the flow path of the fluid between theinlet opening and the outlet opening.

If in this connection the inside diameter of the tubular body isselected to be larger than the outside diameter of the metal bellows tosuch a degree that the inside cross section of the flow path formed bythe annulus is greater than or equal to the inside cross section of theinlet opening and outlet opening, fluid flow rates as large as possiblecan be implemented without significant throttling.

Accordingly, it is advantageous to make the arrangement such that thecover of the metal bellows is fixed on the inside wall of the tubularbody by way of a support structure whose structural elements aredesigned with respect to minimization of throttling on the flow pathbetween the annulus and adjacent outlet opening. For this purpose thesupport structure can have a retaining ring which is fixed on the insidewall of the tubular body and with which the cover of the metal bellowsis connected by way of attachment rods which extend from the side edgeof the cover to the retaining ring. For a correspondingly slenderconfiguration of the retaining ring and fastening rods, the flowresistance is only little.

In order to limit the working movement of the piston part which drawsout the metal bellows, if, for example, there is no fluid systempressure and the gas chamber is prefilled with the working gas, there isa stop means for interaction with the piston part.

Analogously to the support structure which fixes the cover of the metalbellows, the stop means can also be formed by a structure whosestructural elements are chosen with respect to minimization of thethrottling of the flow path caused by them. For this purpose there canbe a retaining ring which is fixed on the inside wall of the tubularbody and at least one fastening rod which spans the interior of theretaining ring.

The working gas with which the working chamber is prefilled is, forexample, nitrogen gas (N₂). In addition, the gas chamber can be filledwith an additional amount of an alcohol, preferably ethylene glycol. Asa result the volume of the gas chamber can be additionally reduced forpurposes of precision adjustment.

For a correspondingly sufficient additional amount of alcohol, aprotective function arises for the metal bellows, i.e., before thepiston part, for example, at an overpressure in the fluid system,strikes the cover of the metal bellows, a protective liquid cushionforms between the piston part and the cover.

The invention is detailed below using one embodiment which is shown inthe drawings.

FIG. 1 shows a longitudinal section of one embodiment of the pressureaccumulator according to the invention,

FIG. 2 shows a perspective oblique view of only the damper unit which isprovided within the accumulator housing of the embodiment of FIG. 1,seen essentially in the direction of viewing indicated by arrow II inFIG. 1; and

FIG. 3 shows a perspective oblique view of the damper unit whichcorresponds to FIG. 2, seen essentially in the direction of viewingindicated by arrow III in FIG. 1.

The embodiment of the pressure accumulator according to the inventionwhich can be used as a pulsation damper shown in the figure has as theaccumulator housing a circularly cylindrical tubular body 1 with alongitudinal axis 3. The tubular body 1 on its inside wall 5 has narrowannular grooves 7 as a seat for snap rings to be described below and oneinside thread 9 each on the two end regions. With these inside threads 9an accumulator cover 11 is screwed on the two ends which are both madethe same and are each sealed by a respective sealing element 13 on thetubular body 1. The accumulator cover 11 which is located at left in thefigure has a central inlet opening 15, while the accumulator cover 11located at right in the figure has a corresponding outlet opening 17 forthe fluid whose pressure fluctuations are to be damped.

In an arrangement which is concentric to the longitudinal axis 3, in theinterior of the tubular body 1 there is the damper unit which is shownseparately in FIGS. 2 and 3 and which in the latter figures isdesignated as a whole as 19. An essential component of the damper unitis a metal bellows 21 in the form of a bellows of circularly cylindricalshape, which is shown in FIG. 1 in the fully extended state whichcorresponds to the largest volume of the gas chamber 23 located withinthe metal bellows 21. Instead of an expansion bellows, a membranebellows which is not detailed could also be used; it has appropriatelyarranged membrane pairs instead of folds located over one another. Toform a housing-mounted termination of the gas chamber 23, one end 25 ofthe metal bellows 21 is welded to a cover 27. On its other end 29, themetal bellows 21 is welded to the piston part 31 which forms a movabletermination of the gas chamber 23 and in the accumulator housing canexecute an axial working movement which leads to volume changes of thegas chamber 23 and of the fluid chamber 33 which surrounds the damperunit 19.

The cover 27 is fixed by way of a support structure on the inside wall 5of the tubular body 1. This support structure has a retaining ring 35which is locked by means of a snap ring 37 which sits in theaforementioned annular groove 7. The retaining ring 35 in turn isconnected to the side edge of the cover 27 by way of attachment rods 39.

As is apparent from FIG. 1, the piston part 31 has the shape of a cupwhose circularly cylindrical side wall 41 extends into the interior ofthe metal bellows 21, the immersion depth into the interior beingdependent on the piston position in the working movement of the pistonpart 31. As mentioned, the piston part 31 in FIG. 1 has the end positionwhich corresponds to the largest volume of the gas chamber 23, thepiston part 31 with its open cup edge adjoining the rods 43 which formpart of the stop means. This stop means is formed by a similarstructure, as is also used as a support structure for the cover 27,i.e., the retaining ring 45 is locked by means of a snap ring 47 in theannular groove 7, the rods 43 analogously extending from the inside edgeof the retaining ring 45 to the fastening rods 39 on the retaining ring35.

The cover 27 has a central fill port 49 via which the gas chamber 23 canbe provided with prefilling which consists of a working gas,specifically N₂, and an additional amount of an alcohol, preferablyethylene glycol.

Since the two accumulator covers 11 have only one opening, specificallyan inlet opening 15 and an outlet opening 17, there can be a largeopening cross section so that large flow rates can be achieved. So thata large volumetric flow can flow through the accumulator housing withoutnoticeable throttling, the inside diameter of the tubular body 1 and theoutside diameter of the metal bellows 21 are chosen such that asufficiently large annulus 51 is available as part of the flow pathwhich belongs to the fluid chamber 33. Accordingly, the components ofthe support structure for the cover 27 are also chosen such that thereis no major obstruction of the flow path, i.e., both the retaining ring35 and also the fastening rod 39 are made slender, as shown in thefigures, so that flow can take place around the outer edge of the cover27 relatively unobstructed. The corresponding applies to theconfiguration of the stop means for the piston part 31 which with theslenderly made retaining ring 45 and slender rods 43 does not form anoticeable flow resistance.

Because the accumulator housing is formed by a simple tubular body 1,and housing termination takes place by means of identically madeaccumulator covers 11, production is especially simple and economical.Since the damper unit 19 can be prefabricated as a unit which can beinserted as a whole into the tubular body 1 and can be fixed by means ofsnap rings 37, 47, installation is especially simple. The damper unitprefabricated as a modular unit consists in particular of the actualmetal bellows 21 as well as the piston part 31 and the retaining ring35.

At a corresponding prefilling amount there is a protective function forthe metal bellows 21, i.e., before the piston part 31 with its freefront side strikes the facing surface of the cover 27 of the retainingring 35, a layer of liquid forms between the indicated parts. In thisway pressure which continues to rise could be precluded from compressingthe metal bellows 21 radially.

In the state prefilled with gas, the piston part 31 is supported on thestop means 43 with its fastening rods and the metal bellows 21 is at itsmaximum extension. In this state it is laid out such that it definitelycan accommodate the internal prefilling pressure of the gas. In allother operating states the metal bellows 21 is in a mostlypressure-equalized state. Depending on the system pressure and the gastemperature prevailing in it, between the lower and the upper extremepoint the bellows will be able to dampen or eliminate all pressurefluctuations for which it is designed by taking up or discharging fluid.This working principle then corresponds to that of a classicalhydropneumatic pressure accumulator used as a damper.

The stop means 43 with its fastening rods is used to support the pistonpart 31 to the extent the system pressure drops below the prefillingpressure within the metal bellows assembly, formed from componentsincluding the metal bellows 21, piston part 31, retaining ring 35 and(gas) filling port; this can occur, for example, when the metal bellowsaccumulator 21 is prefilled with nitrogen. The support of the free frontside of the piston part 31 enables free flow through the accumulatormeans even if the system pressure should be less than the prefillingpressure; the piston part 31 cannot block the fluid opening 15 in thecover 11 in any case.

1. A pressure accumulator, in particular a pulsation damper, having anaccumulator housing (1) which defines a longitudinal axis (3) and whichhas an inlet opening (15) and an outlet opening (17) for a fluid, twoworking chambers, in particular a gas chamber (23) for the working gasand a fluid chamber (33), within the accumulator housing (1) areseparated fluid-tight, in particular gas-tight from one another by abellows-like separating element (21), and the separating element (21) onits one end (25) is connected to a cover (27) which forms ahousing-mounted termination of the gas chamber (23) and on its other end(29) is connected to a piston part (31) which is axially movable in theaccumulator housing (1), and which forms a movable termination of thegas chamber (23) so that working movements of the piston part (31) causevolume changes of the working chambers which border the separatingelement (21), characterized in that there are an inlet opening (15) andan outlet opening (17) on one and the other ends of the accumulatorhousing (1) respectively which are opposite in the axial direction sothat fluid can flow through the accumulator housing (1) in itslongitudinal direction and in the direction of the working movement ofthe piston part (31).
 2. The pressure accumulator according to claim 1,wherein the separating element is a metal bellows (21) which has aplurality of folds or membrane pairs located over one another, and whichin its interior borders the gas chamber (23) between the cover (27) andthe piston part (31).
 3. The pressure accumulator according to claim 2,wherein the piston part (31) on its side bordering the fluid chamber(33) has a cavity which enlarges the volume of the fluid chamber.
 4. Thepressure accumulator according to claim 3, wherein the piston part (31)is made cup-shaped with a circularly cylindrical side wall (41) whichextends into the circularly cylindrical interior of the metal bellows(21) along the inside of its folds with an immersion depth of variedmagnitude according to the working movements of the piston part (31). 5.The pressure accumulator according to claim 4, wherein the filterhousing is a circularly cylindrical tubular body (1) in which the metalbellows (21) is concentrically held with the formation of an annulus(51) between the inside wall (5) of the tubular body (1) and the outsideof the metal bellows (21) and the annulus (51) forms part of the flowpath of the fluid between the inlet opening (15) and the outlet opening(17).
 6. The pressure accumulator according to claim 5, wherein theinside diameter of the tubular body (1) is selected to be larger thanthe outside diameter of the metal bellows (21) to such a degree that theinside cross section of the flow path formed by the annulus (51) isgreater than or equal to the inside cross section of the inlet opening(15) and outlet opening (17).
 7. The pressure accumulator according toclaim 6, wherein the cover (27) of the metal bellows (21) is fixed onthe inside wall (5) of the tubular body (1) by way of a supportstructure (35, 39) whose structural elements are designed with respectto minimization of throttling on the flow path between the annulus (51)and adjacent outlet opening (17).
 8. The pressure accumulator accordingto claim 7, wherein the support structure has a retaining ring (35)which is fixed on the inside wall (5) of the tubular body (1) and withwhich the cover (27) of the metal bellows (21) is connected by way ofattachment rods (39) which extend from the side edge of the cover (27)to the retaining ring (35).
 9. The pressure accumulator according toclaim 8, wherein there is a stop means (43, 45) for limiting the workingmovement of the piston part (31) which enlarges the volume of the gaschamber (23).
 10. The pressure accumulator according to claim 9, whereinthe stop means (43, 45) is formed by a structure whose structuralelements are chosen with respect to minimization of the throttling ofthe flow path between the inlet opening (15) and the annulus (51), whichthrottling is caused by the structural elements.
 11. The pressureaccumulator according to claim 10, wherein the stop means is formed by aretaining ring (45) which is fixed on the inside wall (5) of the tubularbody (1) and by at least one fastening rod (43) which extends betweenthe regions of the retaining ring (45) which are essentially oppositeone another.
 12. The pressure accumulator according to claim 1, whereinthe gas chamber (23) in addition to being filled with working gas, isfilled with an alcohol, preferably ethylene glycol.